Ice Bed Research Articles

An assessment of fluting and “till esker” formation on the foreland of Sandfellsjökull, Iceland

Intensive sedimentological analysis of tills, parallel-sided flutings, and a conduit fill (till esker) on the recently deglaciated foreland of Sandfellsjökull (a temperate, actively receding piedmont lobe draining the eastern margin of the Mýrdalsjökull ice cap in southern Iceland) reveals that subglacial sediment was emplaced predominantly as a dilatant A horizon after an initial phase of glacitectonite production from local outwash. Clast macrofabric strengths weakened through time, presumably in response to increasingly wetter substrate conditions, until the emplacement of the fluted till when clast alignment was more tightly constrained. The fluting phase was initiated only after boulders were plucked from an adjacent bedrock cliff and lodged at the ice–till interface. This suggests that the parallel-sided flutings constrained shearing at the ice–bed interface in a similar fashion to a fault gouge, thereby strengthening clast alignments but allowing the till to mould around larger obstacles to produce herringbone fabric patterns. Strong clast macrofabric strengths in the till esker are not parallel to the ice flow direction, but instead align parallel with the local axis of the meandering ridge. This suggests that the till esker was likely produced by the squeezing of a dilatant till into an elongated cavity or R-channel after meltwater evacuation, followed by localized deformation, constrained by the channel walls, as the channel moved downvalley because of ice flow. The short period over which the deformation took place was enough to impart weaker fabrics in parts of the conduit that lie transverse to the ice flow direction and stronger fabrics where the conduit trends toward parallelism with the ice flow.

Experimental and thermal analysis of washing the packed ice bed in wash columns

AbstractIn the process of freeze concentration (FC), the main problems in operating the counter‐current wash column used for separating ice from ice slurries are channeling and viscous fingering. These phenomena lead to the mixing of pure water and mother liquid, as well as entrainment of mother liquid within the removed ice. Experimental and thermal analysis of the wash front interface in this research relates ice melting and wash front breakthrough with the operating conditions (such as the wash water temperature, ice bed temperature and porosity). Criteria for wash front stability are proposed. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Bed of ice

Edward King and colleagues towed a radar system over Antarctic ice, and whiled away Christmas in a tent, in their quest to understand glacier sliding.

Correction to “Variations of ice bed coupling beneath and beyond ice streams: The force balance”

[1] In the paper ‘‘Variations of ice bed coupling beneath and beyond ice streams: The force balance’’ by T. Hughes (Journal of Geophysical Research, 114, B01410, doi:10.1029/2008JB005714, 2009), Table 1 and Figure A1 are corrected and the following text corrections. [2] In Figure 3 caption, change 1 8> 0. [3] At the end of paragraph 27, change fI = wF/wI = P*W/ PI to f = wF/wI = P*W/PI. [4] Rebreak first two rows of equations in paragraph 66 as follows:

Meltwater discharge through the subglacial bed and its land‐forming consequences from numerical experiments in the Polish lowland during the last glaciation

AbstractNumerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady‐state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice‐sheet‐thickness‐modulated, down‐ice‐decreasing hydraulic heads. In relation to non‐glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice–bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo‐ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice–bed interface. Owing to the abundance of low‐permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright © 2009 John Wiley & Sons, Ltd.

Factors influencing the basal temperatures of a High Arctic polythermal glacier

AbstractA number of glaciers in the Canadian High Arctic are composed primarily of cold ice, but the ice at or near their beds reaches the pressure-melting point (PMP) in the ablation zone. Past modelling studies have suggested that the basal temperatures of some of these glaciers reach the PMP where they should not, indicating that they are not in thermal equilibrium with present-day surface air temperatures. To investigate the possible reasons for thermal disequilibria in such glaciers, a two-dimensional ice temperature model was used to simulate the inferred thermal characteristics of John Evans Glacier, Ellesmere Island. Results indicate that while surface refreezing and historical ice-thickness changes have had a warming effect upon basal ice temperatures, supraglacial meltwater reaching the glacier bed provides the single most critical heat source for explaining the apparent thermal disequilibrium between present-day inferred ice–bed temperatures and those modelled under present-day boundary conditions.

Spatial variation of radar-derived basal conditions on Kamb Ice Stream, West Antarctica

AbstractRadar profiles of bed echo intensity can survey conditions at the ice–bed interface and test for the presence or absence of water. However, extracting information about basal conditions from bed echo intensities requires an estimate of the attenuation loss through the ice. We used the relationship between bed echo intensities from constant-offset radar data and ice thickness to estimate depth-averaged attenuation rates at several locations on and near Kamb Ice Stream (KIS), West Antarctica. We found values varying from 29 dBkm–1 at Siple Dome to 15 dBkm–1 in the main trunk region of KIS, in agreement with a previous measurement and models. Using these attenuation-rate values, we calculated the relative bed reflectivity throughout our KIS surveys and found that most of the bed in the trunk has high basal reflectivities, similar to those obtained in the location of boreholes that found water at the bed. Areas of lower bed reflectivity are limited to the sticky spot, where a borehole found a dry bed, and along the margins of KIS. These results support previous hypotheses that the basal conditions at locations like the sticky spot on KIS control its stagnation and possible reactivation.

Variations of ice bed coupling beneath and beyond ice streams: The force balance

A geometrical force balance that links stresses to ice bed coupling along a flow band of an ice sheet was developed in 1988 for longitudinal tension in ice streams and published 4 years later. It remains a work in progress. Now gravitational forces balanced by forces producing tensile, compressive, basal shear, and side shear stresses are all linked to ice bed coupling by the floating fraction ϕ of ice that produces the concave surface of ice streams. These lead inexorably to a simple formula showing how ϕ varies along these flow bands where surface and bed topography are known: ϕ = hO/hI with hO being ice thickness hI at x = 0 for x horizontal and positive upslope from grounded ice margins. This captures the basic fact in glaciology: the height of ice depends on how strongly ice couples to the bed. It shows how far a high convex ice sheet (ϕ = 0) has gone in collapsing into a low flat ice shelf (ϕ = 1). Here ϕ captures ice bed coupling under an ice stream and hO captures ice bed coupling beyond ice streams.

Interactions between Structure H Hydrate Formers and Water Molecules

Studies on methane storage in hexagonal structure H (sH) hydrates reveal that hydrate stability conditions, formation rates, and cage occupancies differ for the three large molecule guest substances (LMGSs) studied: tert-butyl methyl ether (TBME), neo-hexane (NH), and methyl-cyclohexane (MCH). In this work, the structures of aqueous solutions with the LMGS are examined with molecular dynamics to gain insights into the interactions between water and LMGS. Water molecules form solvation cavities that follow the contours of the LMGS molecules and have diameters between 4 and 7 Å. The cavity size increases from TBME < NH < MCH, and the nearest water molecules to the LMGS have a local density that is higher by a factor of 2 than that of the bulk water phase. Water molecules interact strongly with the ether oxygen of TBME but not with other atoms in the LMGS molecules. This strong attraction gives TBME a greater solubility in water and better wetting on ice than NH or MCH. Moreover, TBME also has a larger diffusivity than NH in water. The greater contact between TBME and the host water molecules may cause the faster rate of initial hydrate growth from solid ice particles (fixed bed) or liquid water with mixing for this guest species. However, the strong attraction of the TBME molecule with water may also slow down the subsequent crystal growth and may perhaps limit the occupancy of the other guests (methane) in the sH clathrate. The volume change due to solvation is negative for all three LMGSs. This suggests a more compact hydrogen bond network in the hydration shell that may facilitate the formation of clathrates when a hydrate seed is available and when mass and heat transfer resistances are negligible. For example, this may occur during hydrate formation from a fixed ice bed with temperature ramping. Hence, the clathrate growth with hydrophobic guests (NH and MCH) proceeds rapidly toward completion as the temperature is increased above the ice melting point. On the other hand, the formation of hydrate cages for the TBME system is disrupted because of the strong water−solute interactions. Consequently, hydrate formation from ice with thermal ramping with TBME is slower.

Gross Vulval Edema After Laparoscopic Instillation of 4% Icodextrin Solution

Severe vulval edema after laparoscopic ovarian cystectomy with instillation of adhesion-prevention solution (4% icodextrin) is a rare complication. A 17-year-old girl was readmitted to the hospital 2 days after laparoscopic ovarian cystectomy with massive vulval swelling, pain, and anxiety. Gross swelling was potentially caused by accumulation of fluid 4% icodextrin in the labia. The condition resolved spontaneously with application of ice packs and bed rest. Possible mechanisms of this complication are discussed as is the importance of adequate counseling and consent before surgery when adhesion prevention solutions are to be administered.

A laboratory study of particle ploughing and pore-pressure feedback: a velocity-weakening mechanism for soft glacier beds

AbstractIf basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice–bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15–400 m a−1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a factor of 3.0–6.6 with a six-fold increase in ploughing velocity. Characteristic timescales of pore-pressure diffusion and compaction down-glacier from ploughing particles depend on till diffusivity, ploughing velocity and sizes of ploughing particles. These timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred. Existing ploughing models do not account for velocity weakening. A new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38% but requires that excess pore pressures be measured. Velocity weakening by this mechanism may affect fast glacier flow, sediment transport by bed deformation and basal seismicity.

Experimental study of wash columns used for separating ice from ice-slurry

The separation of ice from ice slurries is the final step in the process of freeze concentration, where wash column can be employed. Phenomena found in washing an ice bed, such as channeling, viscous fingering, clogging, liquid entrainment, and permeability were studied in an experimental wash column. The appropriate operating conditions that lead to a successful washing were proposed in this paper.

Diurnal fluctuations in glacier ice deformation: Haut Glacier d'Arolla, Switzerland

AbstractMeasurements of surface velocity, ice deformation (at 42 and 89% ice depth) and proglacial stream discharge were made at Haut Glacier d'Arolla, Switzerland, to determine diurnal patterns of variation in each. Data are analysed in order to understand better the relationship between hydraulically induced basal motion and glacier ice deformation over short timescales. The data suggest that hydraulically induced localized basal ‘slippery’ spots are created over diurnal cycles, causing enhanced basal motion and spatially variable glacier speed‐up. Our data indicate that daily glacier speed‐up is associated with reduced internal deformation over areas previously identified as slippery spots and increased deformation in areas located adjacent to or down‐glacier from slippery spots. We interpret this pattern in terms of a transfer of mechanical support for basal shear stress away from slippery spots to adjacent sticky areas, where the resulting stronger ice–bed coupling causes increased ice deformation near the bed. These patterns indicate that basal ice is subjected to stress regimes that are variable at a high spatial and temporal resolution. Such variations may be central to the creation of anomalous vertical velocity profiles measured above and down‐glacier of basal slippery zones, which have shown evidence for ‘plug flow’ and extrusion flow over annual timescales. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Polar Radar for Ice Sheet Measurements (PRISM)

We provide an overview of a project to develop and demonstrate radars for imaging the ice–bed interface, mapping shallow and deep internal layers, and measuring ice thickness. We developed an ultra-wideband very high-frequency (VHF) radar (120 to 300 MHz) for simultaneously measuring ice thickness, mapping internal layers at depth, and imaging the ice–bed interface, and an ultra high-frequency (UHF) ultra-wideband radar (500 to 2000 MHz) for fine-resolution mapping of near-surface internal layers. We used these radars to collect data at Summit Camp, Greenland, during July 2005, and the West Antarctic Ice Sheet (WAIS) deep drill core site during January 2006. These results provide us with an unprecedented view of basal characteristics and internal layers. We also developed an outreach program, a communications system, and rovers to facilitate geophysical measurements in the future.

Seasonality of the late Pleistocene Dawson tephra and exceptional preservation of a buried riparian surface in central Yukon Territory, Canada

The late Pleistocene Dawson tephra was deposited by one of the largest Quaternary eruptions in northwestern North America. Its distribution is known sparsely from sites near the source area in southwestern Alaska and central Yukon Territory, where more than 20 occurrences are documented in the Klondike region. Dawson tephra erupted about 25 , 300 14 C yr BP , near the onset of the last glaciation, and provides a stratigraphic marker across Eastern Beringia. We report radiocarbon ages, paleobotanical data, and cryostratigraphic observations from a new Dawson tephra locale at Goldbottom Creek, in the Klondike region of Yukon Territory, which collectively indicate that the eruption occurred in the late winter or early spring. Multiple, fining-upward tephra-rich ice beds are interpreted as remnants of surface icings, which presently are common in the region during spring. A buried in situ riparian meadow, preserved below the icing and tephra, consists of abundant tufted hair grass ( Deschampsia caespitosa), with interspersed horsetails ( Equisetum cf. palustre) and mosses. Detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits, consistent with a late season surface when the icing was active. The extraordinary thickness of Dawson tephra in central Yukon likely reflects reworking of a winter-deposited tephra by snow melt in the spring following the eruption, indicating that the primary thickness may be overestimated at valley-bottom sites. Winter deposition of the tephra may have, in part, minimized the terrestrial ecological impacts of the eruption on zonal “steppe-tundra” vegetation through the retransportation of tephra from hillslopes to the riparian areas, where the tephra became incorporated into local fluvial systems.

A critical assessment of subglacial mega-floods: a case study of glacial sediments and landforms in south-central Alberta, Canada

The existing subglacial megaflood explanation of glacial sediment deposition and landform production in south-central Alberta relies upon four sets of observations and associated interpretations: (1) a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt-out till or “ice stagnation facies”; (2) a melt-out genesis for the “ice stagnation facies”; (3) a syn-depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice–bed re-coupling; and (4) a subglacial megaflood origin for a “truncation surface” and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area. We provide alternative interpretations of the sediment-landform assemblages of the area and demonstrate that alternative, simpler interpretations of the evidence can be proposed. Specifically, we propose: (1) a proglacial rather than subglacial origin of glacilacustrine sediments; (2) a glacilacustrine origin for the “melt-out till” and its subsequent glacitectonic disturbance by minor glacier readvances; (3) postdepositional rather than syn-depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments; (4) that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting; (5) that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic, because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time. Truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water. The mega-flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis-aligned and cross-cutting flow sets terminating at series of inset and locally cross-cutting and lobate transverse ridges (moraines). These landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines. The similarity of the glacial landforms of this region to the active, temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments, where sheetfloods have not been influential in subglacial landform production, allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding.

Time-dependent basal stress conditions beneath Black Rapids Glacier, Alaska, USA, inferred from measurements of ice deformation and surface motion

AbstractObservations of surface motion and ice deformation from 2002–03 were used to infer mean stress fields in a cross-section of Black Rapids Glacier, Alaska, USA, over seasonal timescales. Basal shear stresses in a well-defined zone north of the center line (orographic left) were approximately 7% and 16% lower in spring and summer, respectively, than in winter. Correspondingly higher stresses were found near the margins. These changes in the basal shear stress distribution were sufficiently large to cause mean surface velocities to be 1.2 and 1.5 times larger in spring and summer than in winter. These results were inferred with a simple inverse finite-element flow model that can successfully reproduce bulk surface velocities and tiltmeter data. Stress redistribution between the well-defined zone and the margins may also occur over much shorter time periods as a result of rapidly changing basal conditions (ice–bed decoupling or enhanced till deformation), thereby causing large variations in surface velocity and strongly influencing the glacier’s net motion during summer.

Evidence for excess pore‐water pressure generated in subglacial sediment: Implications for clast ploughing

Pore water pressure in front of an object pulled through subglacial sediment and water pressure at the base of a borehole were simultaneously recorded at Unteraargletscher, Switzerland, to investigate the generation of excess pore pressures downglacier from ploughing clasts. Analysis of the strongly correlated pressure records revealed that the amplitude of the pore‐pressure fluctuations was larger than that of the corresponding borehole pressure fluctuations. Guided by high temporal resolution measurements of glacier surface motion from a different year, this finding suggests that temporal changes in glacier speed lead to changes in the degree of excess pore‐pressure in front of the ploughing object. The generation of excess pore water pressure has the potential to weaken the sediment downglacier from ploughing clasts. Instead of these clasts providing the roughness at the ice–bed interface to resist glacier motion, the ploughing process may in fact help to decouple the ice from the bed reducing basal resistance.

Application of radar and seismic methods for the investigation of temperate glaciers

The capabilities of seismic and radar methods for the study of ice sheets have been analysed by other authors in the past. The joint use of both techniques has allowed the comparison of information, such as ice thickness, retrieved from both sources. Though these methods, specially the radar sounding, have also been widely used for the study of polythermal and temperate glaciers, the literature lacks joint analysis of their use for the study of temperate glaciers, where physical processes absent in the cold ice masses come into play. We have used seismic and radar methods collected at Johnsons Glacier, a temperate ice mass located in Livingston Island (Antarctica), to show the glaciological information that can be retrieved from such data. The aspects considered include the determination of ice thickness, the retrieval of information concerning the internal structure of the glacier (distinction between accumulation and ablation zones, determination of the depth of the firn–ice transition, detection of buried crevasses), the estimation of physical parameters such as seismic and radio wave velocities, water content in temperate ice and firn density, and the use of radar and seismic data to infer the presence of water channels at the ice–bed interface and to determine the nature of subglacial sediments.

The origins of glacially related soft-sediment deformation structures in Upper Ordovician glaciogenic rocks: implication for ice-sheet dynamics

In the upper Ordovician glaciogenic rocks of West Gondwana, many soft-sediment deformation structures are attributed to glaciotectonic processes. However, little is known about the subglacial and ice-marginal processes associated with this ice sheet. A systematic description and interpretation of these soft-sediment deformation structures is supplemented by a comparison with Late Quaternary and Modern glacial settings to provide qualitative constraints on the character of ancient subglacial thermal regimes. Soft-sediment striations were formed by discontinuous, shear-induced deformation beneath an ice sheet that oscillated between warm and cold-based thermal regimes. Beneath warm-based ice, coupling across the ice–bed interface was poor with sliding and loading occurring at this surface. Loading of soft, waterlogged sediments allowed the development of fluted surfaces, which are also associated with the formation of truncated folded zones. During times of cold thermal regimes, coupling across the ice–bed interface was enhanced by freezing, which caused changes in the position of the freezing front. These discontinuous changes, coupled with sustained subglacial shearing, resulted in the development of stacked, soft-sediment striated surfaces. In areas where the subglacial substrate had an irregular topography, complex shear zones formed that comprised stacked duplex systems interlayered with highly strained units preserving pervasive, folded lineations. At the ice front, large glaciotectonic deformation structures (comparable with push moraines) developed during sustained periods of (re)advance that created composite thrust and fold systems. Deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance. Other deformation structures include dome-like folds that consist of central anticlines (30 to 70 m in width) with tight rim synclines that formed by the load-induced, diapiric intrusion of muds. An ice-sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs. These surges potentially caused the widespread reorganisation of a glacial load resulting in the pro- to subglacial extrusion of soft sediments.